This invention pertains generally to switching between several Private Branch Exchange units (PBXs), and more particularly to an adjunct software-configured system for performing such switching within a wide-area network.
A Private Branch Exchange (PBX) is an automatic telephone switching system that enables users within an organization to place calls to each other without going through the public switched telephone network (PSTN). Many large organizations require the deployment of numerous PBXs to cover their organization.
Although an organization could connect each of their PBXs to the PSTN, and then rely on the PSTN in order to interconnect their PBXs, this approach is not always preferred. Leased tie lines between sites are generally expensive. Since the organization usually maintains a Wide Area Network (WAN) for data communications between its various buildings and sites, it would be preferable if PBX-to-PBX communications could be routed across the WAN.
FIG. 1 shows an example of one configuration for connecting PBXs across a WAN. Four PBXs A, B, C, and D connect to WAN 16. Each PBX connects directly to one of switches 18, 19, 20, and 21, typically through one or more E1 or T1connections. Switches 18, 19, 20, and 21 communicate with each other using Frame Relay packets, ATM (Asynchronous Transfer Mode) cells, or another common WAN packet technology.
In order for the PBXs to communicate across WAN 16, a mesh of Permanent Virtual Circuits (PVCs) is set up between them. For instance PVC 22 connects PBXs A and B via a dedicated connection; likewise, PVC 24 connects PBXs C and D, PVC 26 connects PBXs A and C, and PVC 28 connects PBXs A and D. Although a Virtual Circuit only allocates a physical circuit when there is data to send, a PVC is similar to a dedicated private line because the connection is set up on a permanent basis.
A tradeoff exists between the number of PVCs that are set up between PBXs and the percentage of WAN bandwidth consumed. Although it may be practical to fully mesh the four PBXs of FIG. 1, with larger PBX networks partial meshing makes more sense in order to conserve bandwidth. Thus the PBXs of FIG. 1 are demonstrated as partially meshed. Although a caller on PBX A may directly contact a party attached to any of the PBXs, a caller on PBX B has no PVC directly available to a party attached to PBX C or PBX D.
With no direct PVC, it may still be possible for the caller to indirectly contact PBX C or D, by going through PBX A and using two tandem PVCs. But the use of tandem PBXs wastes PBX and WAN resources. It also generally precludes the use of a voice compression codec, or at least limits compression to one of the PVCs, as tandem encodings dramatically degrade sound quality.
The present invention allows existing packet/cell based PVC networks to function as dynamically-switched multi-service networks. An adjunct processor is attached to a network node, and software-configured to service the needs of one or more PBXs that are also tied to a network node. The service capability offered by the software-configured adjunct processor allows PBXs to establish voice and data connections between each other dynamically via Switched Virtual Circuits (SVCs) that are routed directly across a WAN. This arrangement eliminates the need for an extensive mesh of PVCs or leased xe2x80x9ctie linesxe2x80x9d carrying voice and data traffic between PBXs across the WAN. It also eliminates the need for routing connections in multiple hops between PBXs. Yet another advantage is that the number of physical interfaces required on the PBXs and the attached switches is reduced. Also, the adjunct processor approach generally requires no modification to the PBX software in order to interoperate with the PBX.
In one aspect, the present invention comprises a computer-readable medium containing a call processing/routing program for a voice network switching (VNS) system. This program has a switched circuit manager to set up and tear down switched virtual circuits on a multiple-switching-node wide-area network. The program also has a signaling process to exchange call signaling information with a private branch exchange connected to one switching node of the wide-area network and with a remote signaling endpoint. The program further has a call processor in communication with the switched circuit manager and the signaling process. The call processor determines a wide area network destination for a wide area network-routed call originating at the private branch exchange, based on call signaling information from the signaling process, and requests a switched virtual circuit, from the switched circuit manager, to service the wide area network-routed call. Preferably, the switched circuit manager is one execution thread of an administrative process that also monitors the WAN switching nodes attached to PBXs in the VNS service area. Also preferably, the administrative process also provides for communications with a standby VNS (or an active VNS if this one is in standby), and/or for communications with a network management system.
In a further aspect of the invention, a method of operating a voice network switching system connected in a wide-area network is disclosed. A first software process is configured to exchange call signaling information with a private branch exchange connected to a switching node of the wide-area network. The first software process is also configured to determine a wide-area-network destination, for a call originating at the private branch exchange, based on the call signaling information. A second software process is configured to establish and manage a switched virtual circuit between the node and the wide-area-network destination. A message path is provided between the first and second software processes. The first software process uses the message path to request the switched virtual circuit between the node and the wide-area-network destination, and the second software process uses the message path to notify the first software process when the switched virtual circuit has been established.